Dewaxing of lubricating oil



W. N. AXE

DEWAXING OF LUBRICATING OIL Filed April 10, 1950 Nov. 8,v 1955 A T TO/PNE KS isa-c United States Patent DEWAXING or LUBRICATING ouJ William N. Axe, Bartlesville, kla., assigner to Phillips Petroleum Company, a corporation of Delaware Application April 10, 1950, Serial No. 155,062

8 Claims. (Cl. 196-19) This invention relates to the dewaxing of lubricating oil stocks. In one aspect, it relates to a process for dewaxing lubricating oil stocks for the production of low pour point oils without the use of extremely low dewaxing temperatures. In another aspect, it relates to a method for dewaxing lubricating oil'stocks in which relatively hightemperatures in comparison to those ordinarily used in dewaxing operations can be used for the'production of low pour point oils.

The dewaxing of lubricating oils is an old and well known art. Many processeshave been practiced for lowering lthe pour point of lubricating oils in order to facilitate maintenance of liquidity 'of the oil at relatively low temperatures. Lubricating oils for internal combustion engines are frequently 'dewaxed to produce oils having pour points of about 0 F. in order to provide lubricants ywhich are fluid under cold weather conditions.

Flow of oil through the engine is thus assured over a ltemperature range from engine starting temperatures to normal operating temperatures. For oils used' in colder climates the pour point should preferably be below 0 F. and dewaxing to a pour `point below 0 F. may be necessary. In addition to ldewaxing, pour point depressauts may be v'added to 'at leastl partially dewaxed oils in order to assist in obtaining the desired pour point without 'removal of all of thewaxes otherwisey necessary. The

presence of waxes in lubricating oils ordinarily increases the viscosity index 'of the oils. K Y

Of the methods known for removing wax `from oils 'twocommonly' practiced methods are solvent dewaxing andv propane dewaxing. Y In solventvde'waxing, the oil is mixed with a solvent,

forexampleA methyl isobutyl ketone, and thewmixture is subsequently chilled to a temperature at which suicient w'ax precipitates to yield an oil which, when separated from rthey precipitated wax and thesolvent, has the desired 'pour point. The temperature kto which thesolventoil solution must be cooled is approximately the ydesired pour point temperature lof 'the finished oil.

In propane dewaxing of oilsl a solution of propane and a waxy oil is chilled, for eiiample by vapc'ir'izati'on of the portion of the'propane, to cause precipitation of the amount of wax'necessary to impart the desired'xpour point'to the recovered llubricating oil.A The wax maybe separated from the propane-oil solution, forexample by filtration or `settling.` The propane is vaporizedfrorn the oil for recovery of the iinished dewaxe'd oil'. One undesirable feature of thep'ropane *dewaxing process is the necessity for chilli-ng vthe propane-oil solution to'a temper'atu'r'e well below the desired pour point of the finished oil. `For example, it inay be 'necessary to chill a propaneoil solution tov F. inorder to `dewax a lubricating oil to a pour point of 0 F. Asecond diflicul'ty of the propane dewaxing process' is the tendency of a propaneoil solution'tosupercool witlrthe attendant inconvenience in having `to induce 'crystallization'o'fthe wax.

It has `recently been found that urea will react with nparaflns to form solidcomplexes or addition products.

ICC

Since the waxes of petroleum origin are principally nparainns, urea will form addition compounds with these wax hydrocarbons and consequently dewaxing may be effected by such complex formation. This invention combines propane dewaxing with the formation of addition compounds between urea and n-paraflins for the efcient dewaxing of lubricating oils. The process comprises in general the steps of precipitating wax froma lubricating oil-propane solution by chilling, 'forming solid urea-n-hydrocarbon addition compounds with the remaining waxy components, ltering the combined solid material from the oil-propane solution and recovering the lubricating oil from the filtrate.

The process may be practiced in any of several modifications. The advantages, operational features and improvement in results depend somewhat upon the particular embodiment of the invention practiced. Among the advantages obtained are provision of alter aid manufactured in the process to facilitate wax iiltration, producing a stable seed for seeding the wax precipitation step and effecting satisfactory pour point lowering with less refrigeration. Many other advantages will` be realized upon reading the following disclosure. The procesa may be carried out either continuously or batchwise.

The chemistry of the formation of the addition complexes between urea and the nhydrocarbons is not well understood.

It has been found that urea forms addition products approximately in the ratio of one. mol of ureafor each LCHzgroup in a n-hydrocarbon; the end methyl groups apparently do not enter into the reaction. In many instances, however, less than one'mole of urea per methylene group enters into the reaction, forA example, urea reacts with n-hexadecane inthe mole ratio of about 11:1. Maximumyields of addition compoundsare obtained in many cases at temperatures of from 0 to 100 F., as for example, about F. on 'one hour contact time. However,'maximum yields are frequently obtained under other temperature and time conditions. Contact times as short as one minute give substantial reaction in many cases. Due to .the Vinstability of the urea-hydrocarbon complex, higher temperatures usually give lower yields while lower temperatures also give lower'yields due to'lower lrates of reaction. To compensate for the lower rate `of reaction at lower temperatures, it may be advisable Vto 'use'an excess of urea in orderl to increase the rate of formation "of addition compounds, or lto: in'- crease 'the lengthof contact time, or both'. For the production of',automotive4 lubricants complete yremoval of then-paraiins is not necessary and usually is even undesirable,y so reasonable rates of complex formation are usually attainable by tliese of an 'excess of urea; u The presence of'an l'activator increases the rate..of complex'fo'rination to a marked degree. Thela'rnountwof activatorused mayy vary over a relatively large range of concentration. However, excessive amounts of activator should be" avoided. The ureaand the activator may be 'added :to the 4oiljto be dewaxed as a saturated solution of urea in activator, as 'an activator-urea slurry or as solid urea'merely wet with the activator. 4An excessive amount of'activator is no tjdesirable. Since theac'tivato'rs are solvents `for urea, large amounts will decompose the addition product byV dissolving the urea. `Decomposition of the urea paraffin complex mayunder certain conditions beaceo'mplished bythe addition of suiiic'ient activator material to dissolve vkthe urea. Y p 4 vrThe use of excessiveamounts of diluent materials with they oil undergoing Idewaxing l'frequent times slows 'down the fate A"of formationo'f the urea-normalparatlin coin'- plex and therefore excessive amountsI of diluehts should not 4be used.' Diluen't's, such as pentaiie, but'ahe, propane, thane y'or 'iso'paraiiins,` which compounds do no'treact with urea to form addition products at reaction ternperatures, may be used to an advantage in some instances, such as in urea reactions with waxes which are solids, at the desired reaction temperature. Materials which may be used as activators are such as methanol, ethanol, acetone, methyl ethyl ketone and low molecular Weight ethers, such as dimethyl ether, diethyl ether, or methyl ethyl ether.

The drawing represents schematically an arrangement of apparatus parts for carrying out the process of my invention. Referring now to the drawing, a waxy lubricating oil stock from a source not shown enters the system through line 10. A mixture of urea and activator, such as methanol, is passed through line 11 into the oil flowing through line 10. The urea added at this point is preferably solid urea wetted with the methanol. rom about l to l weight per cent of the urea-methanol mixture is added to the oil. Liquid propane from line 56 is added to this stream of oil, urea and methanol. Part of this propane may be recycle propane and pass through lines 52 and 55 into line 56, or the propane may originate from a source, not shown, and be introduced into the system through a line 57. After the system is in operation, usually only make-up propane is introduced through the line 57. Thus the propane from line 52 with any propane added through line 57 passes through lines 55 and 56 into the charge stock owing through line 10. The total amount of propane added from line 56 to the oil stream in line 10 should preferably be from 21/2 to about 5 times the volume of the oil. This charge stock mixture ows from line through valve 13 and pipe 14 into a chilling zone 15. In this chilling zone 15, chilling is preferably accomplished by evaporating a portion of the propane. Accordingly, sufcient propane is evaporated from chiller under the influence of the suction of the pump 53 acting through pipe 51 so that the temperature of the charge material in chiller 15 is decreased to a value between the limits of about 0 F. and 60 F. After sufficient time has passed that the wax has been precipitated in the chiller as wax crystals or as urea-wax complexes, or both, the material is passed on through conduit 16 to a wax separation zone 17. In this zone 17, all solid material including wax and wax-urea complex is separated from the oil-propane solution. Separation may be effected by settling or preferably by filtration through most any suitable type of mechanical filter. The separated solid material from zone 17 is passed through conduit 18 to an exchanger or heater 19 in which the solid material is heated suiciently to melt the wax and to decompose the wax-urea complex. The urea may, however, remain as a solid. The efuent from the heater 19 then passes on to a urea recovery apparatus 20 in which solid urea is separated from the melted n-paran waxes at a temperature above the urea-n-parain complex formation temperature. This recovery unit 20 may be a filter or other separation means suitable for the separation of solid urea from the molten waxes. The liquid waxes are removed from the separator 20 through a line 22 for such disposal as desired. The recovered urea and activator are passed through conduit 21 into the conduit 11 from which it flows as recycle urea into the charge stock passing through line 10. Methanol as needed may be added to the urea flowing from conduit 21 into conduit 11 from conduit 11A from a source, not shown. The urea may be transferred as a slurry with propane if desired, not shown.

The dewaxed oil-propane solution from the wax separation zone 17 is passed through line 30 into a propane recovery zone 31. In this zone, the propane is vaporized from the oil by any means desired. The separated propane is passed through line 52 and is added to the propane passing through line 51 on its way to the suction side of the compressor or pump 53. The compressor 53 compresses the propane to such a pressure that on passage through the condenser 54 condensation to liquid d occurs. Liquid propane then passes from the condenser 54 on through line 52 to be recycled through lines 55 and 56 into the oil charge line 10. The dewaxed propane-free oil, as the main product of the process, is passed from the recovery unit 31 through line 40 to storage or such other disposal as desired.

In the chiller 15, precipitation of wax occurs along with the formation of urea-n-parain complexes with additional waxy material. Thus, by this combination of wax removal steps occurring in zone 15, the oil recovered through line 40 has an abnormally low pour point. Or, if it is desired to produce an oil having a conventional pour point, as for example 0 F. to -20 F., the cooling or refrigeration of zone 15 need not be carired so far. Thus, the cost of the chilling operation for zone 15 is considerably decreased since the contents of this zone need not be cooled to such a low degree to produce an oil having a given pour point. Some addition product formation ordinarily occurs in lines 10 and 14. These adducts act as crystallization initiators in zone 15.

The exchanger or heater 19 may be operated at a temperature within the range of about 130 to 170 F. The minimum temperature for the operation of this heater is that at which the wax melts and the urea-n-paratn complexes decompose.

The n-parain compounds separated from the urea in the recovery unit 20 at a temperature above which the complex will reform and passing through conduit 22 may, if desired, be further processed to separate higher-melting wax from lower-melting wax. Such a separation may be accomplished by dissolving the wax in a solvent, such as pentane, and contacting this solution with a solution or slurry of urea in methanol to form a solid filterable addition complex of a higher-melting wax which may be separated by filtration. A deficiency of urea is used in this case, so that only part of the wax hydrocarbons form addition compounds. The separated complex is then heated to its decomposition temperature for recovery of a wax melting at a higher temperature than the wax material charged into this latter wax-urea complex formation step. The unreacted wax separated as iltrate is accordingly a lower-melting wax. Other wax solvents than pentane may be used, such as urea treated kerosene, benzene, toluene, or similar compounds, as well as other paraffinic hydrocarbons having 2 to 4 carbon atoms per molecule, i. e., ethane, propane or butane.

In another embodiment of my invention, the urea-nparain complex formation is carried out using a partially dewaxed oil as the charge stock. In other words, the charge oil may be partially dewaxed in a conventional propane dewaxing operation and the dewaxing completed with the use of urea. In this embodiment. liquid propane from line 56 is added to a waxy oil stock owing through line 10 and the mixture is passed on through valve 13 and line 14 into the chilling zone 15. In this chilling zone 15, suicient propane is evaporated to reduce the temperature of the remaining liquid to any desired wax precipitation temperature. Cold oil-propanewax mixture is passed through line 16 to the wax separation zone 17 in which the solid wax is removed from the oil-propane solution. The oil-propane solution is then passed on through line 30 into zone 31 in which a portion of the propane may be removed from the oil, if desired. The remaining oil-propane solution, still containing some Wax, is passed from zone 31 through line 33 and valve 37 into the precipitation zone 34. This zone 34 is ordinarily operated at a considerably higher temperature than is the wax precipitation zone 15. For example, zone 34 may be operated at substantially atmospheric temperature. Solid urea moistened with methanol or a urea-methanol slurry is introduced into this precipitation zone 34 from a source, not shown, through line 35, and from line 51A. In this zone 34, precipitation of the urea-n-parain complex takes place, and the complex separated by settling or filtration from the oil-propane solution. Also included in zone 34 may be a final propane separation stage in which final traces of propane are removed from the waxfree oil so that a lubricating oil product having a desired pour point `may be passed Athrough line 36 `to such use or other disposal as desired. If desired, all of the propane may be removed from the partially dewaxed oil in the propane removal .zone 31 so Ythat -the oil passing through line 33 and yvalve37 vinto vthe precipitation zone 34 will be free from propane and a propane removal step will then not need to be included in the zone 34.

The separated vurea-paraffin complex material from separation zone 34 Yis .passed through lines 38 and 41 and through valve 41A .into line 16 upstream of the wax separation zone .17. The solid urea-n-parafiin complexes added tothe oil .containing precipitated wax in suspension flowing through li'ne 16 is intended to become well mixed with the oil -fiowing through this latter line. When the mixture is filtered in the separation or filtration zone 17, this solid complex material acts as a filter aid and assists -in the filtration of the wax precipitate from the oil-propane solution. In this manner, filtration rates in zone 17 are considerably higher than when complex material is not so utilized. Some of the urea-paraffin complex material from line 38 may be passed through a valve 38A on through line 43 into conduit 14 which is upstream of the chilling zone 15. In this manner, solid urea not utilized in complex formation in zone 34 may assist in the primary dewaxing operation in the chilling zone 15 while that portion of the complex and urea passing through line 41, valve 41A and line 16 into the separation zone 17 serves as a filter aid as mentioned.

The solid material separated in separation zone 17 which consists of parafiin wax, solid urea and urea-nparafiin complex is passed from the filter or separation zone 17 through line 18, heater 19 and into the urea recovery zone 20. In the heater 19, the solid complex material and the wax precipitate are intended to be decomposed or melted. The only material remaining as a solid in the effluent from the heater 19 is the solid urea and this solid urea leaves the urea recovery unit 20 through the line 21. In this embodiment, this urea recovered in unit 20 may be passed through line 51A to be added to the urea-paraffin complex precipitation zone 34. The temperature in the recovery unit 20 is maintained above that at which urea-n-complexes form so that reformation of such complexes will not occur.

In still another embodiment of my invention, the urean-paraiiin addition complexes are formed prior to the cooling and wax precipitation operation. In this embodiment, to the waxy oil flowing through the line are added the urea-methanol mixture from line 11 and propane from line 56. In this case, valve 13 is closed and valve 27 in line 28 is opened so that the mixture may flow directly into the urea-paraffin complex formation zone 12. Valve 42 in line 29 is also opened so that the solution of oil and propane containing urea and ureaparaffin complex in suspension may pass through line 29, valve 42 and line 14 into the chilling zone 15. In this zone 15, sufiicient propane is vaporized to cool the remaining liquid to a desired dewaxing temperature. From the chilling zone 15, the oil-propane solution containing the urea-paraffin complex and any excess of solid urea is passed through conduit 16 to the separation Zone 17, and from this point on the separation and recovery of the urea, wax, oil, and propane are the same as have been described hereinbefore.

If in any o f the operations it is desired to add activated urea directly into the chilling zone 15, a line 52A is provided.

In the process of this invention, propane dewaxing and urea-n-parafiin complex formation co-operate in an advantageous manner. Only a limited amount of urea is ordinarily used. The urea removes the paraffin compounds that are normally not removable by conventional propane dewaxing. The urea-n-parafin complexes func- 6 tion `as .a filter aid in the filtration of wax .in separation zone 17 as mentioned above.

As mentioned hereinbefore, one ydisadvantage `of conventional propane dewaxing is the tendency of thechilled propane waxy oil ksolution to supercool. It has been found that these urea-n-,paraiiln complexes act as seed or crystallization inducing materials for the precipitation of wax from cold waxy oil-propane solution. Thus, as mentioned above, some complex is passed from line 38 through valve 38A and on through lines 43 and 14 yinto the wax precipitation zone 15. In this manner, supercooling of the oil-propane solution is .brought to an end and wax precipitation is normal.

Specific examples As an example illustrating the utility of urea lfor dewaxing of oils, the following operation was carried out. A 5W oil which has .been propane dewaxed to a 150 F. pour point is further dewaxed at about 70 F. b y urea activated with methanol. After removal ofthe urean-parafiin complex material from the so treated oil, the resulting ,oil -has a pour point below 50 F.

According to one of the embodiments described hereinbefore, the urea-n-parafhn complex separated from the oil having a pour point below 50 F. is added to the propane dewaxer eiuent to act as a filter aid in the wax filtration step. The filtering characteristics of the wax are substantially improved over those of the dewaxer efiuent without the presence of the urea-n-paraiiin complex.

The above described flow diagram and examples are given for illustrative purposes -and should not be regarded as limiting the invention, the scope of which is set forth in the following claims.

Having described my invention, I claim:

l. A process for producing low pour point lubricating oil stocks from high pour point waxy lubricating oil stock comprising mixing the waxy oil stock with liquefied propane, chilling the mixture to a dewaxing temperature and thereby crystallizing wax, admixing with this oil-propanewax mixture a quantity of urea-n-paraiin wax complex as subsequently produced, separating the admixed complex and crystallized wax from residual oil-propane solution still containing some wax in solution, warming this latter solution to a temperature between about 0 and F. and above said dewaxing temperature, mixing with this warmed solution an admixture of solid urea Wet with an activating agent comprising a low molecular weight oxygen containing aliphatic compound selected from the group consisting of alcohols, ketones, and ethers, removing from this latter admixture a urea-n-parain wax complex thereby leaving a dewaxed oil solution containing propane, recovering the oil from this dewaxed oil solution containing propane as the dewaxed oil product of the process and returning the removed urea-n-parafiin wax complex to the first admixing step as said urea-nparain wax complex as subsequently produced.

2. The process of claim l wherein said low molecular weight oxygen containing aliphatic compound is methanol.

3. The process of claim 1 wherein said low molecular weight oxygen containing aliphatic compound is methyl ethyl ketone.

4. The process of claim 1 wherein said low molecular weight oxygen containing aliphatic compound is ethanol.

5. The process of claim l wherein said low molecular weight oxygen containing aliphatic compound is acetone.

6. The process of claim l wherein said low molecular weight oxygen containing aliphatic compound is diethyl ether.

7. A process for producing a low pour point lubricating oil stock from a high pour point waxy lubricating oil stock comprising mixing the oil stock with liquid propane, chilling the mixture to a dewaxing temperature, admixing with the chilled mixture a quantity of solid urea wetted with a low molecular weight oxygen-containing aliphatic compound selected from the group consisting of alcohols, ketones and ethers, separating the admixture into a fraction of solid material and a fraction of liquid material, recovering dewaxed oil of a lower pour point than that of the original waxy oil stock from the separated liquid material as one product of the process, dividing the separated solid material into two portions, returning one portion to the separating operation as a lter aid, and recovering wax from the other portion as a second product of the process.

8. A process for producing a low pour point lubricating oil stock from a high pour point waxy lubricating oil stock comprising mixing the oil stock with liquid propane, chilling the mixture to a dewaxing temperature, admixing with the chilled mixture a quantity of solid urea wetted with methanol, separating the admixture into a fraction of solid material and a fraction of liquid material, recovering dewaxed oil of lower pour point than that of the original waxy oil stock from the separated liquid material as the main product of the process, dividing the 2 separated solid material into two portions, returning one portion to the separating operation as a lter aid and recovering wax from the other portion as a second product of the process.

References Cited in the file of this patent UNITED STATES PATENTS 2,026,336 Wilson Dec. 31, 1935 2,229,659 Carr Jan. 28, 1941 2,248,668 Gee `luly 8, 1941 2,499,820 Fetterly Mar. 7, 1950 2,546,328 Arabian et al Mar. 27, 1951 2,560,193 Shoemaker July l0, 1951 2,569,984 Fetterly Oct. 2, 1951 2,588,602 Adams et al. Mar. 11, 1952 2,606,140 Arnold et al. Aug. 5, 1952 OTHER REFERENCES 

1. A PROCESS FOR PRODUCING LOW POUR POINT LUBRICATING OIL STOCKS FROM HIGH POUR POINT WAXY LUBRICATING OIL STOCK COMPRISING MIXING THE WAXY OIL STOCK WITH LIQUEFIED PROPANE, CHILLING THE MIXTURE TO A DEWAXING TEMPERATURE AND THEREBY CRYSTALLIZING WAX, ADMIXING WITH THIS OIL-PROPANEWAX MIXTURE A QUANTITY OF UREA-N-PARAFFIN WAX COMPLEX AS SUBSEQUENTLY PRODUCED, SEPARATING THE ADMIXED COMPLEX AND CRYSTALLIZED WAX FROM RESIDUAL OIL-PROPANE SOLUTION STILL CONTAINING SOME WAX IN SOLUTION, WARMING THIS LATTER SOLUTION TO A TEMPERATURE BETWEEN ABOUT 0* AND 100* F. AND ABOVE SAID DEWAXING TEMPERATURE, MIXINGING WITH THIS WARMED SOLUTION AN ADMIXTURE OF SOLID UREA WET WITH AN ACTIVATING AGENT COMPRISING A LOW MOLECULAR WEIGHT OXYGEN CONTAINING ALIPHATIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALCOHOLS, KETONES, AND ETHERS, REMOVING FROM THIS LATTER ADMIXTURE A UREA-N-PARAFFIN WAX COMPLEX THEREBY LEAVING A DEWAXED OIL SOLUTION CONTAINING PROPANE, RECOVERING THE OIL FROM THIS DEWAXED OIL SOLUTION CONTAINING PROPANE AS THE DEWAXED OIL PRODUCT OF THE PROCESS AND RETURNING THE REMOVED UREA-N-PARAFFIN WAX COMPLEX TO THE FIRST ADMIXING STEP AS SAID UREA-NPARAFFIN WAX COMPLEX AS SUBSEQUENTLY PRODUCED. 